This project is a follow-on to a clinical trial for the "Management of Hyperbilirubinemia in the Newborn". The original objective of the clinical trial was to test inhibitors of heme oxygenase (HO) to moderate hyperbilirubinemia in preterm infants, thereby reducing or eliminating the need for phototherapy and exchange transfusions. This follow-on will determine the safe, effective dose(s) of Sn-mesoporphyrin (SnNP), as well as the appropriate time(s), when this HO inhibitor should be given to be most effective clinically. The follow-on will also determine, in term infants with jaundice from a variety of causes, whether SnMP can control the subsequent rate of increase of plasma bilirubin concentration to the extent that the need for phototherapy is obviated.